cmd: Kconfig: LED command depends on LED subsystems

Without CONFIG_LED, we get

cmd/built-in.o: In function `show_led_state':
cmd/led.c:40: undefined reference to `led_get_state'
cmd/built-in.o: In function `do_led':
cmd/led.c:99: undefined reference to `led_get_by_label'
cmd/led.c:108: undefined reference to `led_set_state'
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>

cmd/Kconfig

@@ -1399,6 +1399,7 @@ config CMD_DISPLAY
 
 config CMD_LED
 	bool "led"
+	depends on LED
 	default y if LED
 	help
 	  Enable the 'led' command which allows for control of LEDs supported